The present invention relates to a nail gun, and more particularly, to the nail gun electrically or pneumatically operated for providing a fine appearance on a workpiece after nail fastening.
Attachment members or finishing materials for use in a baseboard for trimming purposes or for a verandah running on more than two sides of a house or room are adhesively fixed to a wall, and then fixed by fasteners such as nails. A groove having a predetermined small width such as from 3.5 to 7 mm is formed in the attachment member, and the nails are driven into the groove. The nails have a head portion whose color is selected to be in conformance with the external color of the attachment member. Further, the head portion of the nail has a small diameter, so that the head portion can be positioned onto a bottom of the small width groove in an attempt to obtain good external appearance on the attachment member without any scratches as bruises after the nail driving.
As shown in FIGS. 1 and 2, a conventional nail gun includes a main body 1 and a contact arm 5 having a tapering end portion 5A adapted to be in pressure contact with a workpiece such as the attachment member 9. The contact arm 5 has another end portion 5B adapted to push a trigger plate 3A. A valve plunger 4 can be pushed up upon manipulation of a trigger 3 as far as the trigger plate 3A is in the pushed up position. The contact arm 5 is normally biased by a spring 6 toward the attachment member 9. That is, the contact arm 5 is movable relative to the main body 1. When the contact arm 5 and the trigger 3 are both operated, a nail driving operation can be started.
The tapering end portion 5A has an accurate and thin tip end so that it can be positioned onto the bottom of a narrow groove 91 of the attachment member 9. The tapering end portion 5A can serve for sharpshooting the nail to a desired location, since the nail is driven in a direction along a length of the tapering end portion 5A.
The conventional nail gun is also provided with a nose portion or bit guide 7 positioned in side by side relation to the contact member 5. The nose portion 7 is formed with a nail supply passage 7a and an injection passage 75 in communication therewith. Alternatively, the injection passage 75 can be formed at a boundary between the contact arm 5 and the nose portion 7. A drive bit (not shown) can pass through the injection passage 75. Upon driving the drive bit, the nail passes through the injection passage 75 and is driven into the attachment member 9.
A magazine 2 is provided for accommodating a plurality of nails 8. Further, a spring-biased feeder (not shown) is provided in the magazine 2 for feeding the nails 8 to the nail supply passage 7a. The contact arm 5 directly receives the biasing force of the feeder.
If the tapering end portion 5A is pressed onto the attachment member 9 against the biasing force of the spring 6, the contact arm 5 is moved relative to the main body 1, so that the other end portion 5B of the contact member 5 pushes the trigger plate 3A upwardly. By pressing the trigger 3, the valve plunger 4 is moved, so that compressed air is supplied into a cylinder (not shown) through a trigger valve (not shown) so as to drive the drive bit toward the attachment member 9, to thus drive the nail into the attachment member 9.
The total thickness of the tip of the nose portion 7 and the tip of the tapering end portion 5A must be as small as possible, so that these tips can be positioned in the narrow groove 91. On the other hand, these tips must have a sufficient thickness for providing a given mechanical strength. In considering these conflicting requirements, the total thickness of these tips is selected to be about 4 mm. If the width of the groove 91 is smaller than the total thickness, the conventional nail gun is not available, and instead, a punch must be used.
If the tip end face of the tapered end portion 5A and the tip end face of the nose portion 7 can be positioned in the groove 91, the nail 8 can be accurately driven into the groove 91. On the other hand, if the width of the groove 91 is approximately equal to the total thickness of the tip ends, or is smaller than the total thickness, the nail may not be driven into the groove area but is driven into an improper portion of the attachment member 9.
Nail driving is repeatedly and rapidly performed with short intervals, since a great number of nails must be driven. An operator uses the tip end of the tapering end portion 5A to aim the nails. When performing rapid nails driving, the operator may inadvertently insert only the tip end of the tapering end portion 5A into the narrow groove 91. That is, only the tapering end portion 5A reaches the groove bottom, whereas the tip end of the nose portion 7 is positioned outside of the groove 91 as shown in FIG. 2. If nail driving is performed in such a condition, the nail head may not be positioned onto the groove bottom.
Further, in such a conventional nail gun, its center of gravity is positioned on or around the trigger lever 3. During nail driving, the nail gun may jump up due to the reaction force, and the gun may be urged to rotate about its center of gravity, so that the tip of the nose portion 7 may be offset frontwardly as shown by an arrow A in FIG. 1. Thus, the downwardly moving drive bit may become offset from the nail 8, and hit the surface of the attachment member 9. Even though the tapering end portion 5A is urged downwardly (toward the attachment member) by the biasing force of the spring 6 in spite of the upward movement or jumping of the gun, the nose portion 7 is moved upwardly by the reactive force, and further, the tip portion of the gun is rotated in the direction A. Consequently, the driven nail 8 is not properly aligned with or positioned in the injection passage 75 but becomes offset therefrom. Accordingly misalignment occurs between the nail and the drive bit. Thus, the surface of the attachment member 9 is spoiled with a bruise, and the nail 8 is insufficiently driven.
Furthermore, there is a probability that the end face of the tapering end portion 5A may not reach the groove bottom if the groove 91 is deeply formed. In the latter case, the contact arm 5 cannot be moved, i.e., the contact arm cannot be lifted against the biasing force of the spring 6, and therefore, the trigger plate 3A cannot be pushed by the other end portion 5B of the contact arm 5.
To avoid the above-described drawbacks, accurate positioning is required for placing the end face of the tapering end portion 5A and the end face of the nose portion 7 onto the groove bottom to provide a complete preparatory work for trigger manipulation. However, such careful work may lower the nail driving efficiency, and prolong the nail driving work.
Moreover, since the spring-biased feeder in the magazine 2 is urged toward the contact arm 5, and since the contact arm 5 must be movably biased toward the attachment member 9 by the spring 6, the spring 6 must provide greater biasing force, otherwise, the biasing force of the feeder toward the contact arm 5 may restrain the moving force of the contact arm 5 toward the attachment member 9. As a result, the contact arm 5 is urged toward the workpiece surface with excessive biasing force, and therefore, the surface of the groove bottom may be injured. Furthermore, due to the excessive biasing force of the spring 6, greater force is required to move the contact arm 5 against the biasing force of the spring 6. Moreover, if the nail gun is accidentally dropped, the thin tapering end portion 5A may be deformed or broken.